Re: contrib/intarray vs empty arrays

From: Greg Stark <stark(at)enterprisedb(dot)com>
To: Teodor Sigaev <teodor(at)sigaev(dot)ru>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Oleg Bartunov <oleg(at)sai(dot)msu(dot)su>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: contrib/intarray vs empty arrays
Date: 2009-04-09 13:29:33
Message-ID: 4136ffa0904090629o1aa3f5daw435b7ff58df9fea9@mail.gmail.com
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2009/4/9 Teodor Sigaev <teodor(at)sigaev(dot)ru>:
> contains - all elements of second array are contained in the first one.
> Empty array has no element, so it can't be contained.

That sounds wrong. A <contains> B should surely always be true if B is
empty. ie "for all x, x in B implies x in A". Or put another way,
"contains" just means "is a superset of" and all sets are supersets of
the empty set (even the empty set).

--
greg

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